I cannot find a picture of your harmonic balancer to know which style you have. Most have an outer ring that is glued to the center hub. Many years ago those lasted the life of the vehicle, but now, for some reason, it is somewhat common for that jelly to let go and the ring can spin on the hub. The place where that usually causes a problem is when there is a timing mark on that ring. That puts it in the wrong place.
Some engines are "externally balanced", meaning there are two counterweights they could not cast as part of the crankshaft. Instead, you will find a small weight welded to the torque converter or flex plate, and weight added to the hub of the harmonic balancer. The only way the heavy spot on the harmonic balancer could shift is if the keyway was broken apart or the key sheared off to allow the hub to rotate on the snout of the crankshaft. That is not common, but eventually the balancer would slip so badly that the serpentine belt would stop driving the generator and power steering pump. You would also feel the slop when you tried to wiggle the balancer.
Some harmonic balancers, mostly on import engines, have the pulley for the serpentine belt cast as part of the outer ring. On those, if that ring slips, eventually it will burn the bonding material away and fall off.
The clue to a mechanical imbalance problem is the vibration will change a lot with changes in engine speed. At idle you might not notice any problem, but at a certain higher speed, (the harmonic), the vibration will get real bad. At a still higher speed it may be less noticeable. Think of the pendulum on a grandfather's clock. There is only one speed at which it takes very little energy to keep it swinging. You have to exert a lot more force to make it swing faster or slower than its normal speed. A crankshaft bends in the middle due to the forces put on it by the connecting rods. There is a happy speed that is its natural speed, just like the clock pendulum, at which very little energy is needed to keep that occurring. However, the actual energy being input by the connecting rods stays constant, so in effect, way more energy than what is needed is being put into it. (As a point of interest, big block Chevy engines that are run real fast, as in around 7,500 rpm, often break into three pieces on the race track due to that bending along with the use of special lightweight harmonic balancers and flywheels). If your engine's happy speed where the vibrations occur is 700 rpm, every multiple of that is a harmonic, meaning the vibration will be worst at 1,400, 2,100, 2,800, etc. Rpm. The harmonic balancer is weighted and designed to dampen those vibrations, and they do a real good job. Even if they did not, you won't break a crankshaft because the forces being put into it are nowhere near what is encountered in a race engine.
Monday, May 16th, 2016 AT 8:38 PM